Tight bass is a myth?

Hi,

No, it's not a myth.

1) The frequency response for the PB12-Plus on SVS site isn't that accurate. Here's a better one by Ed Mullen.



2) Even if the frequency responses would be identical, there are also other variables in play. Two most important are maximum SPL capability and distortion. I haven't yet seen two identical subwoofers when considering these variables, so that's why we'll have different sounding subwoofers. Pretty much equally important factors are in-room frequency response and integration (both FR and SPL) with other speakers because a subwoofer alone can't ever produce tight sounding bass without the help of higher frequencies.

The main contributor to bass peaks and ringing is the room. Yes, some subs ring more than others. But once you get to even medium quality subs, the room is by far the dominant factor. Also, a ported sub may ring at its cut-off frequency, but most rooms have half a dozen or more ringing peaks.

Below is a waterfall graph showing the response and ringing of the PB12-Ultra/2 in my living room. There is very little ringing except at the very lowest length mode. The main reason there's so little ringing is because I have a huge number of bass traps.

--Ethan

Illka...would this happen to be from a database other than your testing?
If so, could you provide a link?
I am trying to figure out the T/S for the SVS 20-39Pci or at least a guesstimated spl graph.(for frame of reference for my first DIY build)

There are several factors that contribute to "tight bass". And NO, it is NOT a myth.

As has been said the room can be a HUGE factor. This includes how solid the walls are, room modes etc.

Freq response has very little to do with how "tight" the bass sounds. In order to have a "tight" sound it must respond quickly and then STOP responding-evenly across the band-including harmonics. Drivers that have a large excursion (front loaded) have to get a lot of mass moving and then attempt to stop it quickly. While horn loaded subs drivers don't move as far to produce the same output, it is much easier to "stop" them after the signal has been removed.

Damping factor is one issue that can help (amps with a high DF-AND large connecting cables)

The other is the actual loudspeaker/sub itself. It must have a smooth phase response and very little group delay. Those are numbers you are not going to get from most (especially home theatre) manufacturers. They are generally more easily gotten by a pro provider. Heck, it is hard enough to get an ACCURATE freq response with sensitivity from a HT manufacturer, much less other info that is much harder to understand the significance of.

There is no magic bullet. In order for YOU to get a good bass sound, it is a combination of the room, equipment (amps-sub-cables) and tuning. It will be different for different peoples rooms.

Hi,

The FR measurement is done by Ed Mullen (currently working for SVS).

The whole review is here: http://www.hometheaterhifi.com/volum...06-part-1.html

Agree. A bad sub usually sounds better in a good room than a good sub in a bad room. And when you combine a good sub and a good room - heaven.

I agree with your post other than the quote above. I would say phase response (and group delay which is derived from it) isn't that important assuming it's not totally out of whack. There are studies showing that people can't hear group delay at low frequencies until it's quite high, higher than on any subwoofer currently available. The threshold raises almost exponentially below ~50 Hz.

No, I said just the opposite. They wouldn't sound identical because of the differences in distortion and maximum SPL capability. Those variables will be in play at pretty much all normal listening levels when using only single subwoofer. If the level would be kept really low, it would be extremely hard to distinguish two subwoofers having identical in-room frequency response (when integration with mains included).

Not necessarily. Measuring the true response of loudspeakers is much more complicated than most people realize, especially at very low frequencies. I'm not in a position to say who "knows more" about how to measure subs, but it's not as easy as sticking up a microphone and measuring sine waves.

Also, and not to indict SVS because I have their PB12 and love it, like most speaker makers they used smoothing in their graph. Since they don't say how much was applied it's impossible to pass judgment. This is from that page on their site:


So it seems they used a similar method as hometheaterhifi.com, but in a quick read I didn't see hometheaterhifi.com state how far their test was from nearby boundaries. If the distances were not identical I'd expect different results.

--Ethan

Damping factor has been debated for 50 years. I wonder at which frequencies the ear is most sensitive to damping factor? I would guess it is not in the range from 80Hz on down, (any more than the ear is as sensitive to other forms of distortion, like THD in the range from 80 Hz on down).

Maybe you don't agree with the 10% THD limit used for many years now by professional testers of subwoofers.

IMHO, damping factor really only comes into play in discussions of tube amps vs. solid state amps. A tube amp might only have a damping factor of 8, yes I said EIGHT. Most solid state amps have damping factors of over one hundred, (100), especially in the critical mid-range.

Bryston only says that the damping factor of its amps is over 500.

Of course there was the Crown Macro Reference with its damping factor of 20,000. IMHO, there is no audible difference between a damping factor of 500 and one of 20,000.

There have been studies done on damping factor. No one could hear any difference between a damping factor of 20,000 and 200.

I don't even want to talk about large cables, unless you are talking about commercial applications where long runs are a necessity.

For most listeners this is all academic. They buy a powered sub. Who knows what the damping factor of a BASH amp is? I would venture to say that the differences in cone weight and the stiffness of the surrround would easily outweigh any difference in damping factor in a powered sub. When someone asks what kind of subwoofer cable they should buy, the large majority on this Forum recommend something inexpensive, such as something from Monoprice.
I understand that once you commit to high end gear, including separate amps for subwoofers, that opens the door to spending lots of extra money on things like "high damping factor" amps and large and expensive connecting cables.

I would suggest that readers take a look at the following paper on damping factor:

http://www.classic-audio.com/marantz...ingfactor.html

He suggests that damping factors under 20 are "pretty poor", while damping factors over 100 are "pretty darned good". Maybe there is a good reason why Bryston only specifies a damping factor of >500.

If anyone asks, I will tell them not to try to power a subwoofer with a tube amp.

I will agree about the damping factor. I just wanted to throw it into "part" of the overall equation. I have seen HT installs that use very small wire and cheap amps-poor connectors etc-so the damping will be a factor in those situations.

What I have heard when comparing different amps is that some pro amps with a lot lower damping factor actually have a tighter low freq those some others with a higher DF. There are other factors (other than DF) that affect the overall tightness of the sound. I think the damping of the "system" (everything other than the amp) is the biggest contributing factor-but the amp will figure in.

Hi

When you speak of what is sounds like one is dealing with subjectivity.
This can add a layer of potential confusion.

For example, in Pro sound it is common to evaluate a subwoofer alone with a signal like a kick drum.
Your ear picks out the one that sounds most like a kick drum, easy.
You ear usually picks the one with a higher low corner and or greater harmonic distortion. Why??? You ear knows what a kick drum sounds like and finds the speaker than produces the closest thing, while the actual subwoofer signal contains say below 80Hz only.
In reality, the subwoofer with more harmonic distortion makes the upper bass register muddy when added to the full system.
So, with that example of how your ear can look for the wrong things at times keep these additional things in mind.

One teeny tiny issue speaker companies don't mention as a selling point is that speakers spread out signals in time, if a single broadband event is fed to the speaker and high frequencies come out first and the lows last.
At low frequencies, the signal may be produced the equivalent of a number of feet behind the upper bass (in time) for example
How much shift there is depends on the shape and slope of the rolloff curve, the steeper the roll off, the greater the phase shift. For that reason, all other things being equal a sealed box often sounds tighter than a vented box and a vented box tighter than a high order bandpass.
Why do these systems exist? The sealed box runs out of linear excursion first, the vented next, a high order bp last.

If the roll off slope has a shape or Q greater than about .6, then there is a longer retention of energy than is idea, a very high Q is like tapping on a Bell for example while a very low Q is like tapping on modeling clay.

Subwoofers are used with other speakers, the crossover used is also a common source for more time spreading.
A similar condition exists here to, the signal emerges from the HF crossover first and the low section last. The lower the crossover, the larger the time delay is between them, the more behind in time the subwoofer signal arrives at the terminals.
The steeper the slope is the larger the time offset is as well.

Group Delay is often cited as a useful measure yet that requires interpretation too.
For example, as one lowers the corner frequency of a woofer, one finds progressively more GD so this is bad right?
No, not necessarily larger measures of Time can correspond simply to a longer period wavelength and nothing is wrong. So, with the same shape Q LF corner, lowering the corner actually reduces the GP higher up in frequency instead.
When or if a speakers GD can be reduced to insignificance for that frequency band, it can even preserve the actual waveshape of the input signal, like a square wave equals a square wave out etc.
As before, one finds the sealed box has the least GD associated with its corner f while the high order BP the most.
As for sound I believe the phase shift associated with each low corner is part of why these sound usually different from each other.

So far as damping factor depending on the woofer, for an 8 ohm driver somewhere between 40 and 80 is where you stop seeing any change in anything by making it higher. Tube amps are fine too as long as the diminished damping still results in a satisfactory corner shape (Q) and you don't want very low frequencies out of the OP transformer at high power.
Anyway, some random thoughts on Bass.

Best Regards
Tom Danley
Danley Sound Labs

its probably also important to consider large voltage behavior, not just small. frequency response is often done with small signal. things change a lot when you increase voltage and the linearity of many things drop.